Used to describe the scene in musicals where people in the street know the words and tune to the song sung by any main character, and instantly know the dance routines including, but not limited to: jumping over barrels, swinging girls in the hair and juggling. This is all despite being total strangers.

This is all supposed to be spontaneous, of course, but naturally - it's actually choreographed

"Oliver! really made me laugh. What did you think of all the choreographed spontaneity?"